Description: This core will provide access to equipment, as well as training in proper usage, for quantitative determinations of fluorescence in living cells. Because some of this instrumentation is expensive and time-consuming to set up, the goal is to provide a common facility to support individual research projects. Two types of equipment in current use will be available in this core: a) A computer-controlled fluorometer for determination of fluorescence in populations of cells, either in suspension or in monolayers; and b) a microscope-based digital imaging system. Both types of equipment will be used by investigators after they have been trained by the Core Director. Investigators from all of the projects have need for these facilities in some form or other.